This won't work with the max on time. It's a bit tricky, but it should work like this:
- Your current PL (PL1) should be Function: AND + Input1: Fill water (AWC only) + Input2: Digital input
- Add a second PL (PL2) with Function: Pulse + Input1: PL1 + Time: The max on time
- Add a third PL (PL3) with Function: AND + Input1: PL2 + Input2: Fill water (AWC only)
- Assign PL3 to the switch channel

The switch channel will then be activated for the specified duration (max on time) as soon as Fill water and the digital input are active, but only as long as Fill water remains active. If you also want the switch channel to be deactivated as soon as the digital input is no longer active, you need an additional PL.